U.S. patent number 4,239,819 [Application Number 05/968,074] was granted by the patent office on 1980-12-16 for deposition method and products.
This patent grant is currently assigned to Chemetal Corporation. Invention is credited to Robert A. Holzl.
United States Patent |
4,239,819 |
Holzl |
December 16, 1980 |
**Please see images for:
( Certificate of Correction ) ** |
Deposition method and products
Abstract
A method of depositing a hard, fine grained metal or semi-metal
alloy is described wherein a volatile halide of the metal or
semi-metal is partially reduced and then deposited as a liquid
phase intermediate compound onto a substrate in the presence of an
alloying gas. The liquid phase deposited on the substrate is then
thermochemically reacted to produce the hard, fine grained alloy.
Also described are products which may be produced by the above
method.
Inventors: |
Holzl; Robert A. (La Canada,
CA) |
Assignee: |
Chemetal Corporation (Pacoima,
CA)
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Family
ID: |
25513692 |
Appl.
No.: |
05/968,074 |
Filed: |
December 11, 1978 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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797059 |
May 16, 1977 |
|
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588390 |
Jun 18, 1975 |
4040870 |
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358110 |
May 7, 1973 |
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Current U.S.
Class: |
427/255.39;
148/278; 148/279; 148/280; 427/253; 427/255.391; 427/255.393;
427/314; 427/318; 428/328; 428/457; 428/469; 428/472; 428/627;
428/640; 428/641; 428/663 |
Current CPC
Class: |
C04B
41/009 (20130101); C04B 41/5053 (20130101); C04B
41/87 (20130101); C23C 16/303 (20130101); C23C
16/32 (20130101); C23C 16/325 (20130101); C23C
16/345 (20130101); C23C 16/38 (20130101); C23C
16/42 (20130101); C23C 16/4481 (20130101); C23C
16/4488 (20130101); C30B 25/02 (20130101); C04B
41/5053 (20130101); C04B 41/4529 (20130101); C04B
41/455 (20130101); C04B 41/009 (20130101); C04B
35/00 (20130101); C04B 41/009 (20130101); C04B
35/52 (20130101); C30B 25/02 (20130101); C30B
29/605 (20130101); C30B 29/605 (20130101); Y10T
428/31678 (20150401); Y10T 428/12576 (20150115); Y10T
428/12674 (20150115); Y10T 428/256 (20150115); Y10T
428/12667 (20150115); Y10T 428/12826 (20150115) |
Current International
Class: |
C04B
41/87 (20060101); C04B 41/50 (20060101); C04B
41/45 (20060101); C23C 16/32 (20060101); C30B
25/02 (20060101); C23C 16/34 (20060101); C23C
16/30 (20060101); C23C 16/448 (20060101); C23C
16/38 (20060101); C23C 16/42 (20060101); C23C
011/08 () |
Field of
Search: |
;427/248R,249,255,226,228,253,248A,248B,314,318
;148/6.3,20.6,6.35,133,16.5,127
;428/332,469,457,472,539,328,553,627,628,629,639,640,662,663 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Smith; Ronald H.
Assistant Examiner: Bell; Janyce A.
Attorney, Agent or Firm: Fulwider, Patton, Rieber, Lee &
Utecht
Parent Case Text
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is a continuation-in-part of application Ser. No.
797,059, filed May 16, 1977, now abandoned, which is a
continuation-in-part of application Ser. No. 588,390, filed June
18, 1975, now U.S. Pat. No. 4,040,870 which is a
continuation-in-part of application Ser. No. 358,110 filed May 7,
1973, now abandoned.
Claims
I claim:
1. A method for depositing a hard, fine grained alloy onto a
substrate, comprising providing a volatile, gaseous halide of a
metal or semi-metal, partially reducing the volatile halide in a
first reaction zone by a gaseous reducing agent or particulate
metal or semi-metal which is the same as the metal or semi-metal of
the volatile halide to be reduced, said first reaction zone having
a first pressure and separated from the surface of said substrate,
flowing said partially reduced halide into a second reaction zone
maintained at a pressure lower than the pressure in said first
reaction zone and containing said substrate, providing a gaseous
alloying agent in said second reaction zone, and depositing a
liquid phase intermediate compound onto a substrate within said
second reaction zone, and thermochemically reacting the liquid
phase on the substrate to produce the fine grained alloy.
2. A method according to claim 1 wherein said metal is selected
from the class consisting of aluminum, zirconium, hafnium,
vanadium, columbium, tantalum and chromium, said semi-metal is
selected from the class consisting of boron and silicon, and said
alloying agent furnishes an alloying element selected from the
class consisting of nitrogen, boron, carbon and silicon.
3. A method according to claim 1 or claim 2 wherein said alloying
agent furnishes oxygen as an alloying element in addition to at
least one of the alloying elements set forth in claim 2.
4. A method according to claim 1 or claim 2 wherein said metal is
aluminum.
5. A method according to claim 1 or claim 2 wherein said metal is
zirconium.
6. A method according to claim 1 or claim 2 wherein said metal is
hafnium.
7. A method according to claim 1 or claim 2 wherein said metal is
vanadium.
8. A method according to claim 1 or claim 2 wherein said metal is
columbium.
9. A method according to claim 1 or claim 2 wherein said metal is
tantalum.
10. A method according to claim 1 or claim 2 wherein said metal is
chromium.
11. A method according to claim 1 or claim 2 wherein silicon is
acting as said metal.
12. A method according to claim 1 or claim 2 wherein boron is
acting as said metal.
13. A method according to claim 1 or claim 2 wherein said alloying
element is boron.
14. A method according to claim 1 or claim 2 wherein said alloying
element is carbon.
15. A method according to claim 1 or claim 2 wherein said alloying
element is silicon.
16. A method according to claim 1 or claim 2 wherein said alloying
element is nitrogen.
17. A method according to claim 1 or claim 2 wherein said hard
alloy is comprised of silicon and carbon.
18. A method according to claim 1 or claim 2 wherein said hard
alloy is comprised of silicon and nitrogen.
19. A method according to claim 1 or claim 2 wherein said hard
alloy is comprised of silicon, nitrogen and oxygen.
20. A method according to claim 1 or claim 2 wherein said hard
alloy is comprised of aluminum and nitrogen.
21. A method according to claim 1 or claim 2 wherein said hard
alloy is comprised of silicon, aluminum, nitrogen and oxygen.
22. A method according to claim 1 or claim 2 wherein said hard
alloy is comprised of zirconium and boron.
23. A method for producing a hard, fine grained alloy on a
substrate, comprising placing the substrate in a chemical vapor
deposition reactor and heating the substrate to a temperature of
between about 650.degree. and about 950.degree. C., providing a
flow in the reactor of a gaseous volatile halide of a metal
selected from the class consisting of aluminum zirconium, hafnium,
vanadium, columbium, tantalum, and chromium, partially reducing the
volatile halide to a lower halide in a first reaction zone by a
gaseous reducing agent or a particulate metal which is the same as
the metal of the volatile halide to be reduced, said first reaction
zone having a first pressure and separated from said substrate,
flowing said lower halide into a second reaction zone maintained at
a pressure lower than the pressure in said first reaction zone,
providing in said second reaction zone a gaseous alloying agent
which furnishes an alloying element selected from the class
consisting of nitrogen, boron, carbon and silicon, and controlling
the substrate temperature, the reactor pressure and the relative
amounts of said metal and said alloying agent to cause the
deposition on the substrate of a compound of said metal which is in
a liquid phase, and thermochemically reacting said liquid phase to
said hard, fine grained alloy.
24. A method for providing a hard fine grained alloy on a
substrate, comprising placing the substrate in a chemical vapor
deposition reactor and heating the substrate to a temperature of
between about 1000.degree. C. and about 1600.degree. C., providing
a flow in the reactor of a gaseous volatile halide of a semi-metal
selected from the class consisting of silicon and boron, partially
reducing the volatile halide to a lower halide in a first reaction
zone by a gaseous reducing agent or a particlate semi-metal which
is the same as the semi-metal of the volatile halide to be reduced,
said first reaction zone having a first pressure and separated from
said substrate, flowing said lower halide into a second reaction
zone maintained at a pressure lower than the pressure in said first
reaction zone, providing in said second reaction zone a gaseous
alloying agent which furnishes an alloying element selected from
the class consisting of nitrogen, boron, carbon and silicon, and
controlling the substrate temperature, the reactor pressure and the
relative amount of said semi-metal and said alloying agent to cause
the deposition on the substrate of a liquid phase intermediate
compound, and thermochemically reacting said liquid phase to a hard
fine grained alloy.
25. A method according to claim 24 wherein said alloying agent
furnishes oxygen as an alloying element in addition to at least one
of the alloying elements set forth in claims 24.
26. A method for depositing a hard fine grained alloy of titanium
and nitrogen onto a substrate comprising, providing a volatile
gaseous halide of titanium, partially reducing said halide to form
a lower halide of titanium in a first reaction zone by a gaseous
reducing agent or particulate titanium, said first reaction zone
having a first pressure and separated from said substrate, flowing
said lower halide into a second reaction zone maintained at a
pressure lower than the pressure in said first reaction zone,
providing in said second reaction zone a gaseous alloying agent
containing nitrogen, depositing a liquid phase intermediate
compound on said substrate and thermochemically reacting said
liquid phase to produce said hard, fine grained alloy.
27. A hard metal alloy produced from a volatile halide of a metal
partially reduced to form a liquid compound containing said alloy
which is deposited onto a substrate and thermochemically reacted to
produce said alloy, said alloy comprised of a metal selected from
the class consisting of aluminum, hafnium, columbium, zirconium and
tantalum, and an alloying element selected from the class
consisting of nitrogen, boron, carbon and silicon, said alloy being
free of columnar crystals and having a crystal structure consisting
of fine and substantially equiaxial grains less than about 1 micron
in diameter.
28. A hard silicon alloy produced from a volatile halide of a
silicon partially reduced to form a liquid compound containing
silicon deposited onto a substrate and thermochemically reacted to
produce said alloy, said alloy comprised of silicon and an alloying
element selected from the group consisting of nitrogen, boron and
carbon, said alloy being free of columnar crystals and having a
crystal structure consisting of fine and substantially equiaxial
grains having an average diameter of less than about 0.25
micron.
29. A hard boron alloy produced from a volatile halide of boron
partially reduced to form a liquid compound containing boron
deposited onto a substrate and thermochemically reacted to produce
said alloy, said alloy comprised of boron and an alloying agent
selected from the group consisting of nitrogen, silicon and carbon,
said alloy being free of columnar crystals and having a crystal
structure consisting of fine and substantially equiaxial grains
having an average diameter of less than about 0.25 micron.
Description
BACKGROUND OF THE INVENTION
This invention relates to the production of hard alloy deposits
which are generally used in the manufacture of heat and wear
resistant parts and cutting tools. More particularly, the invention
relates to the production of deposits of alloys on substrates, or
the production of free standing objects made from a deposit after
removal of said substrate. The deposits of the invention have
physical characteristics which are substantially improved over
those presently known to those skilled in the art.
There have been many efforts in the past to improve the superficial
hardness and strength of heat and wear resistant parts and cutting
materials. It is known that the introducion of certain alloying
elements into the surfaces of wear resistant cutting materials will
improve the hardness of such materials. Exemplary of such elements
are carbon, nitrogen and boron which may be used individually or in
combination with other elements.
The introduction of such alloying agents into the surface of wear
resistant materials has been accomplished by a number of different
methods. One such method is by diffusion of the alloying agents
into the surface of the material. This may be accomplished in a
gaseous environment by a process referred to as "metallizing", or
by a molten salt electrolysis referred to as "metalliding".
Another method which may be used separately from or subsequent to
the aforesaid diffusion method is that of "over-coating" alloys
onto the surface of such wear resistant materials. This involves
the use of such materials as chromium carbide, titanium nitride, or
titanium carbide which are deposited on the wear resistant
materials to a thickness of about 1 to 10 microns, or as much as
several hundred microns. These "over-coatings" may be applied by
any one of the techniques known in the art as flame spraying,
plasma arc spraying, reactive evaporation, sputtering, physical
vapor deposition, or chemical vapor deposition.
The foregoing methods have generally improved the hardness of such
wear resistant materials but have not made any significant
improvement in the toughness or strength of such materials. In
addition, alloys deposited by any of the foregoing materials have
been found to have strengths that are generally less than the same
alloys made by the techniques of forging, casting, or powder
consolidation.
Accordingly, an objective of the invention is to improve the
strength and toughness of such deposits whether they be used as
coatings or as free standing bodies.
Another objective of the invention is to produce deposits of higher
hardness than that achieved by conventional methods.
A further objective of the invention is to provide deposits with
closely controlled compositions on extended areas of surface
thereby to enhance their uniformity and chemical stability.
SUMMARY OF THE INVENTION
The method of the present invention is similar to conventional
chemical vapor deposition, referred to herein as CVD, but is
distinguished therefrom and from said prior art techniques, in that
the present invention produces extremely fine, substantially
equiaxial grains. This is to be distinguished from the grains
produced by CVD and the other prior art techniques which produced
either long columnar grains or large equiaxial grains. The
production of deposits having the relatively fine, substantially
equiaxial grains of the present invention produces wear resistant
coatings which are harder, stronger, or tougher than coatings of
the same materials produced by the aforesaid prior art
techniques.
The grains or crystals produced by the method of the present
invention generally have an average diameter on the order of about
0.1 to 0.25 micron or less, but may range up to about 1 micron in
average diameter. This is to be distinguished from the grain size
produced by the aforesaid prior art techniques which are
substantially greater than 1 micron in average diameter and usually
have average diameters in the order of magnitude of hundreds of
microns.
CVD and the method of the present invention both deposit metal
derived from vaporized metal halides. In CVD, the deposition
generally occurs by completely reducing a metallic halide to
produce a metallic deposit on a substrate. In the method of the
present invention, however, the metallic halide is first partially
reduced in a first reaction zone separated from the substrate, and
then introduced into a second reaction zone provided with an
alloying gas and deposited as a liquid phase intermediate compound
onto the substrate. The formation of the liquid phase intermediate
compound controls the nucleation of the grains and prevents the
formation of large or long columnar grains which are produced by
CVD. The liquid phase intermediate compound is thereafter
thermochemically reacted to produce the hard, fine grained alloy of
the present invention.
The partial reduction of metal halides in a first reaction zone
separated from the substrate--referred to as being "off the
substrate"--and the deposition of a liquid phase intermediate
compound on the substrate, are features lacking in conventional CVD
which exercises less control than the present invention over the
nucleation of the grains. For the sake of convenience and to
distinguish the method of the present invention from CVD, the
method of the present invention is referred to as CNTD which stands
for controlled nucleation thermochemical deposition, a shorthand
expression used by the inventor to refer to his invention.
The CNTD method of the present invention generally is not limited
to the use of metallic halides but also employs volatile halides of
semi-metals. The term alloy is used in its broadest sense herein,
and is meant to include solid solutions, chemical compounds, or
mixtures of solid solutions and chemical compounds.
The term substrate is used herein in its broadest sense and is
intended to include any form upon which the coating is deposited,
whether subsequently used in the bonded condition or dispensed with
after deposition such as a mandrel or die.
The liquid phase intermediate compound contains at least one
alloying agent but may contain more. The thermochemical reaction
which converts said liquid phase to a hard, fine grained alloy is
achieved by pyrolysis or by reaction with the alloying gas,
depending upon the particular intermediate compound deposited on
the substrate.
The metals or semi-metals contemplated for use in practicing the
present invention are capable of forming a volatile halide in
gaseous form as a condition precedent to deposition on the
substrate. The gaseous alloying agents contain suitable elements
selected from the class consisting of boron, carbon, silicon, or
nitrogen, to produce the corresponding boride, carbide, silicide,
or nitride, when alloyed with the metal or semi-metal derived from
the volatile halides. Oxygen may be one of the alloying agents when
more than one alloying agent is used.
Exemplary of the metals for use in practicing the present invention
are aluminum and certain of the transition metals of Groups IVb,
Vb, and VIb, namely titanium, zirconium, and hafnium of Group IVb,
vanadium, columbium, and tantalum of Group Vb, and chromium of
Group VIb.
The semi-metals contemplated for use in practicing the present
invention are boron and silicon. These elements generally behave as
semi-metals, but, when silicon is reacted with an alloying agent
comprises of carbon, nitrogen, or boron, and when boron is reacted
with an alloying agent comprised of carbon, or nitrogen and
silicon, they behave in the same way as metals and produce a hard
alloy as contemplated by the present invention.
The alloying agents contemplated for use in practicing the present
invention may be introduced into the deposition system in a number
of ways. Elemental boron, carbon, or silicon may be combined with a
halogen to produce volatile halides. These halides may then be
injected into the gas stream. Nitrogen may be injected as gaseous
elemental nitrogen, ammonia, hydrazine, or in some cases, as an
amine. Silicon or boron may be introduced as hydrides, such as
silane or diborane. Substituted hydrides, such as trichlorosilane
and methyltrichlorosilane, may also be used as a source of silicon,
and carbon and silicon, respectively. Methyltrichlorosilane may
thus function as a source of the semi-metal, silicon, and as a
source of the alloying agent carbon after partial reduction and
introduction into the second reaction zone.
The alloying agent may also comprise a mixture of separate alloying
agents, and when it does, the resultant hard metal coating may
contain a mixture of alloying elements or it may contain only one
alloying element if the metal or semi-metal has a preference for
reacting with only one of the alloying elements. Thus, when
methyltrichlorosilane is used as a source of the semi-metal
silicon, and the alloying agent carbon, it has been found that when
ammonia NH.sub.3 is also introduced in the second reaction chamber,
the resultant coating has been analyzed to be silicon nitride,
only, without any carbon present, thus demonstrating a preference
of silicon to react with nitrogen rather than carbon.
In addition to the specific metals, and semi-metals and alloying
agents set forth herein for use in practicing the present
invention, this invention is intended to cover the use of any other
element capable of forming a volatile halide or any other alloying
agent having the characteristics as aforesaid, which may be found
by routine testing by one skilled in the art having the benefit of
the teachings of this disclosure.
BRIEF DESCRIPTION OF THE DRAWING
The invention will be more specifically described in connection
with the accompanying drawing, referred to as FIG. 1, which is a
schematic diagram of a chemical vapor deposition apparatus employed
in the practice of the method of the invention.
DETAILED DESCRIPTION OF THE INVENTION
In practicing the CNTD method with the apparatus illustrated in the
FIGURE, the hard deposit of the present invention is made upon a
substrate 11 in the form of a cylindrical rod. The rod 11 is
supported in a work holder or fixture 12 supported from a rod 13
resting on a disc-shaped base 14. The disc shaped base 14 is
supported on a reactor base 15 which is provided with an annular
groove 16 therein.
The reactor is completed by a heat-proof cylindrical walled tube 17
of quartz or similar material which seats in the annular groove 16
and is sealed therein by an annular seal 18. The top of the quartz
tube 17 is closed by an elastomeric stopper 19 of conventional
design removably secured therein. There is therefore defined a
reaction chamber 21 in which the CNTD process takes place.
In order to heat the substrate 11 to the desired temperature, as
will be explained, an induction heating coil 23 is provided
surrounding the outer wall of the glass or quartz tube 17. The
induction heating coil 23 is supported by means not shown and is
provided with leads 25 and 27 to which the induction heating
current is conducted from a suitable source, also not shown.
In order to regulate the pressure within the reaction chamber 21,
the lower wall or base 15 of the reactor is provided with an
opening 29 therein through which a tube 31 is passed. The tube 31
is suitably connected to a vacuum pump 23 and a vacuum gauge 35 is
connected in the line thereto for indicating the pressure within
the chamber 21. By properly operating the vacuum pump 33, the
pressure within the chamber 21 may be regulated as desired.
A gas inlet tube 37 is provided in the elastomeric stopper 19
through a central opening 39 therein. There is optionally provided
at the terminus of the tube 37 within the chamber 21, a porous
basket 41 for purposes subsequently described. The tube 37 is
connected through a plurality of tubes 43, 45, 47 and 49 to
regulator valves 51, 53, 55 and 57 and flowmeters 59, 61, 63 and
65, respectively.
Sources of reactant gas 67, 69, 71 and 73 are connected to the
flowmeters 59, 61, 63 and 65, respectively, for introducing the
desired reactive gases within the chamber 21, as will be
subsequently described.
A gas inlet tube 46 passes coaxially in the tube 37 and through the
porous basket 41 to the region upstream of the substrate 11 in the
reactor. The tube 46 is connected by tubes 47 and 49 to regulator
valves 55 and 57, and flow meters 63 and 65, respectively. Sources
71 and 73 of reactant gases are connected to the flowmeters 63 and
65 for introducing reactant gases through the tube 46 to the
chamber 21.
A gaseous halide of said metal or semi-metal from source 67 flows
through tubes 43 and 37 and enters porous basket 41 which forms a
first reaction zone. This first reaction zone is spaced from the
surface of said substrate and separate from the reaction chamber 21
which constitutes a second reaction zone.
The gaseous halides are partially reduced in the first reaction
zone by a reducing agent which may be in the form of a gas, such as
hydrogen, or in the form of particulate matter 75 suspended in
basket 41. If the reducing agent is a gas, said gas flows into
basket 41 through tubes 45 and 46 from source 69. In either case, a
partial reduction or disproportionation reaction occurs between
said gaseous halide and the reducing agent to produce a lower
halide of said metal or semi-metal. The chamber wall is kept at a
sufficiently high temperature to minimize collection of the lower
halide in the basket 41.
The alloying gas from source 71 flows into chamber 21 through tube
46. The partially reduced halide, as aforesaid, also flows into
chamber 21, and is observed as a fog or smoke passing through the
porous basket 41, forming a halo about the substrate 11 and
depositing a liquid intermediate compound on the surface
thereof.
Argon diluent gas is frequently used in the deposition system to
control the heat flux in the boundary layer adjacent the surface of
the substrate. Hydrogen is also used for this purpose in addition
to its use as a reducing agent. When hydrogen is used as a reducing
agent, partial reduction of the gaseous halides is provided by
regulating the partial pressure of hydrogen within the system to
provide a hydrogen pressure which is generally below the amount
needed for total reduction of the halides. Partial reduction may
also occur by using chips of the metal 75 in basket 41
corresponding to the volatile halide to be partially reduced, i.e.,
titanium chips are used to partially reduce titanium
tetrachloride.
In using the apparatus illustrated in FIG. 1 to deposit a coating
of titanium boride pursuant to the CNTD method of the present
invention, a halide of titanium, such as titanium tetrachloride, is
flowed into the first reaction zone and is reduced to a lower
chloride of titanium. This lower chloride of titanium flows into
the reaction chamber 21 and over the heated substrate 21, where it
is deposited as liquid and reacts with boron trichloride to form a
solid deposit. The existence of this intermediate step has been
demonstrated both by direct observation of the liquid formation on
the surface and by inferential data. Methods of effecting the
partial reduction of titanium tetrachloride are the flowing of the
titanium tetrachloride through a heated bed of titanium chips, or
flowing a mixture of hydrogen and titanium tetrachloride over a
heated surface of inert material such as alumina beads. The
resultant solid deposit is either a smooth vitreous appearing
coating or a fine botryoidal coating.
If the liquid phase intermediate compound is not formed, as, for
example, by directly injecting titanium tetrachloride into the gas
reaction chamber 21 without the necessary high temperature partial
reduction, a typical CVD coarse hexagonal crystal of titanium
boride is deposited. X-ray investigation demonstrates that either
type of deposit is titanium diboride. There is, however, a very
substantial difference in the properties of the deposits made by
the CNTD method as compared to the CVD method. The deposits made by
the CNTD method are extremely fine grain, circa 0.1 micron, are
extremely hard by comparison with those made by CVD. The harder
deposits regularly measure greater than HV.sub.500 4000 and have,
in fact, been measured at hardnesses of over HV.sub.500 6000. The
variation is due to the difficulty in the precise measurements of
the thin coatings of such hard materials. By comparison, a typical
crystalline, or conventional titanium diboride coating has a
HV.sub.500 of between 2800 and 3200. This latter hardness is the
hardness generally accepted in the trade for titanium diboride.
The method of the invention for the deposition of the other metals
and semi-metals disclosed herein is the same as described for the
deposition of titanium boride hereinabove. The following examples
serve to assist in an understanding of the invention. The deposits
described in Examples 1, 2, 5, 6, 8, 9 and 11 to 18 were made
pursuant to the CNTD method of the present invention. The deposits
described in Examples 3, 4, 7 and 10 were not made pursuant to the
present invention and are set forth herein for comparative
purposes.
EXAMPLE 1. TiB.sub.2
High-speed-steel drills having a diameter of 3 millimeters (mm)
were first boronized by passing an 8:1 volume ratio mixture of
hydrogen and boron trichloride over them at a temperature of
950.degree. C. at a pressure of 200 Torr for 15 minutes. The drills
were then racked in a furnace, heated to a temperature of
750.degree. C. and maintained at a pressure of 200 Torr. Titanium
tetrachloride at a flow rate of 100 milliliters per minute (ml/min)
was passed through a bed of titanium chips at the same pressure,
heated to 850.degree. C. Boron tetrachloride at a flow of 400
ml/min and hydrogen at a flow of 800 ml/min. were mixed with the
effluent from the chip bed and passed into the reactor furnace
without cooling. In 40 minutes, a smooth, bright coating of 25
micron thickness adherent to the steel was produced. After coating,
the parts were heated to 1150.degree. C. and rapidly quenched in
hydrogen gas to assure the hardness of the steel at Rockwell-C 65.
The coating had a hardness of 7000 kg/mm.sup.2 when measured with a
500 gram weight on a Vickers hardness tester. The drills
successfully produced 9000 holes in laminated glass fiber printed
circuit board material as compared with 30 holes before failure for
similar drills uncoated. Metallographic sections of the deposit
showed a lamellar deposit.
EXAMPLE 2. TiB.sub.2
Cemented carbide rod of 1.5 mm diameter was coated in a manner
similar to Example 1. No preliminary boronization was conducted.
The titanium tetrachloride at 100 ml/min. and the hydrogen at 100
ml/min. were passed through a bed of alumina beads heated to
700.degree. C. before mixing with the boron trichloride at 400
ml/min. The gas mixture was directly injected into the furnace in
which the drill rod was mounted with the furnace held at
850.degree. C. A coating of 25 microns thickness was made in 30
minutes. The coating was bright, smooth and adherent and had a
Vickers hardness number of 6200 kg/mm.sup.2 measured with a 500
gram weight. The metallographic sections showed the same lamellar
structure.
EXAMPLE 3. TiB.sub.2
The experiment of Example 1 was run again except that the titanium
tetrachloride, hydrogen, and boron trichloride were directly
injected into the furnace without any provision for preliminary
reduction of the titanium tetrachloride. The surface of the carbide
drill rod was slightly discolored but there was no measurable
hardness increase. Metallographic examination showed only a slight
coarsening of the grain boundaries near the surface and no well
defined coating.
EXAMPLE 4. TiB.sub.2
An experiment was run using direct injection of titanium
tetrachloride at 100 ml/min., boron trichloride at 400 ml/min., and
hydrogen at 1600 ml/min. into the reactor furnace. The specimens
were 1.5 mm cemented carbide rods. The furnace was held at
1100.degree. C. and the gases pumped off to maintain 200 Torr.
After 60 minutes a bright coating of 6 microns was achieved. The
coating had well developed columnar hexagonal crystals with a
hardness of 2900 HV.sub.500.
The above Examples 3 and 4 illustrate the necessity for the
reaction of the titanium tetrachloride to form a layer chloride
which is deposited as a liquid in accordance with the method of the
invention. In Example 3, since there was no lower chloride
formation and no possibility of the liquid deposition, no deposit
was effected at the low deposition temperature. In Example 4, the
temperature of deposition was too high to allow liquid deposition
so that the mechanism for the deposit was one of ordinary CVD and
the columnar crystals were in evidence.
EXAMPLE 5. TiC
The process of Example 1 was repeated using 3 mm diameter high
speed steel drills. All conditions were the same except that carbon
tetrachloride at a flow of 400 ml/min was used instead of boron
trichloride. The coating had a hardness of 4500 kg/mm.sup.2 when
measured with a 500 gram weight on a Vickers hardness tester.
Drills did not fail in 1000 hole tests on laminated glass fiber
printed circuit board material.
EXAMPLE 6. TiSi.sub.2
The process of Example 2 was repeated using silicon tetrachloride
instead of boron trichloride. The coating was bright, smooth, and
adherent with a hardness of 1650 HV.sub.500. The metallographic
section showed the lamellar structure, similar to that of FIG.
1.
EXAMPLE 7. TiSi.sub.2
Example 6 was rerun using direct injection of titanium
tetrachloride at 100 ml/min; tetrachloride at 50 ml/min; hydrogen
at 4200 ml/min; and argon at 7000 ml/min. to approximate
conventional chemical vapor deposition techniques. The resultant
deposit at 950.degree. C. to 1000.degree. C. was fine crystalline
in superficial appearance and had a hardness number of 950
HV.sub.500. The cross section showed typical columnar grains.
Examples 6 and 7 show the difference between the method of the
invention, wherein a layered deposit essentially free of columnar
grains is formed from the intermediate liquid layer, and the
conventional chemical vapor deposition method.
In performing the above Examples 1, 2, 5, and 6, the following
reactions are believed to be representative of the deposition
mechanism:
or
In the gas stream plus
On the surface followed by
The TiCl.sub.2 is probably representative of a polymeric material
such as (TiCl.sub.x).sub.y which is a liquid under deposition
conditions.
EXAMPLE 8. CbC
Using a substrate of 1.25 cm diameter round molybdenum bar, an
experiment was conducted to deposit columbium pentachloride at a
flow of 400 ml/min. was passed through a bed of columbium chips
heated to 1200.degree. C. The resultant columbium trichloride was
mixed with 600 ml/min. of hydrogen and 800 ml/min. of carbon
tetrachloride. The mixed gas stream was passed over the substrate
which was held at 900.degree. C. Gases were pumped off to maintain
a pressure of 300 Torr. Columbium carbide was deposited at a rate
of 18 microns per minute for 20 minutes. The deposit has a
HV.sub.500 hardness of 3200. The grain structure was fine and
equiaxial. The average grain size as less than 1 micron. There was
no evidence of columnar crystals. It may be noted that columbium
carbide made by conventional chemical vapor deposition would be
columnar and would deposit at approximately one-tenth this rate at
this temperature.
EXAMPLE 9. TaSi.sub.2
Tantalum silicide was deposited on a carbide disc of 25 microns
diameter by 6 mm thick using a technique similar to Example 4.
Tantalum pentachloride was passed through a heated bed of tantalum
chips at 1200.degree. C. and then mixed with silicon tetrachloride.
The rates of flow were tantalum pentachloride 600 ml/min., silicon
tetrachloride 600 ml/min. and hydrogen 1800 ml/min. 0.5 mm of
deposit was effected in 36 minutes at 950.degree. C. A fine grain
deposit with less than one micron crystallites was obtained free of
columnar orientation. The HV.sub.500 hardness was 1600. The
deposited surface was extremely smooth, having a surface of better
than 4 rms. The only irregularities were a few well rounded
hemispheres which had the appearance of frozen droplets and which
are frequently experienced by the method of the invention.
EXAMPLE 10. TaSi.sub.2
The conditions of Example 9 were reproduced except that the
tantalum pentachloride was not passed through the heated bed of
tantalum chips. After 36 minutes of operation no detectable deposit
was observed on the substrate.
EXAMPLE 11. SiC
Deposits of fine grain silicon carbide were made by the following
method: Silicon tetrachloride at a flow rate of 300 ml. per minute
was mixed with a hydrogen stream of at least 300 ml. per minute and
this mixture passed through a preliminary heated zone of the
reaction chamber such as to heat the mixture to 600.degree. C. A
stream of propane at 68 ml. per min. was then added to the stream
and the mixed gases passed over a resistantly heated tungsten wire
maintained at 1150.degree. C. The total pressure was 500 Torr.
Silicon carbide was deposited on the wire at a rate of 0.25 mm per
hour. This silicon carbide had an average grain size of 0.05
microns, a hardness of 4200 HV.sub.500, and a Rupture Modulus in
bending of 2400 MPa. The as-deposited surface was extremely smooth
and the general appearance, vitreous. X-ray diffraction indicated,
however, that the material was pure crystaline silicon carbide.
Cooled portions of the chamber were covered with a yellow viscous
liquid which contained about 23% silicon and 77% chloride by
weight. The test was repeated using identical conditions except
without preheating the mixed silicon tetrachloride and hydrogen
stream. The silicon carbide was deposited at the same rate except
coarse columnar grains resulted in the deposit and the Rupture
Modulus of the material was 725 MPa. The surface topography now
showed a rough crystalline surface.
EXAMPLE 12. SiC
The experiment of Example 11 was repeated using trichlorosilane as
a source of silicon. Part temperature was held at 1150.degree. C.
and the total pressure at 250 torr. Similar fine grain deposits of
silicon carbide resulted of nearly identical strength and hardness
at a deposition rate of 0.5 mm per hour.
The experiment of Example 12 was repeated using
methyltrichlorosilane as a source of silicon and omitting the
propane from the gas stream with the same results. In all cases,
the yellow viscous liquid was observed. The experiment was repeated
with methyltrichlorosilane without preheating the mixed hydrogen
and methyltrichlorosilane stream. No yellow viscous liquid was
observed. Deposits were all coarse columnar morphology, typical of
chemical vapor deposits. The Rupture Modulus in bending was 860
MPa.
EXAMPLE 13. Si.sub.3 N.sub.4
Using an experimental arrangement identical to that used for
silicon carbide deposits, the following experiment was conducted. A
mixture of silicon tetrachloride at 275 ml. per minute with a like
flow of hydrogen was premixed and heated to 600.degree. C. 100 ml.
per minute of ammonia having been preheated to the same temperature
was then added down-stream of the heater and the total mixture
passed over a graphite rod inductively heated to 1250.degree. C.
The total pressure in the chamber was 75 torr. A deposit of 0.5 mm
thickness of silicon nitride was made on the graphite rod in three
hours. The silicon nitride deposit was composed of crystallites of
less then 1 micron with a smooth botryoidal surface topography. The
material was heat treated at 1500.degree. C. for 3 hours to assure
conversion of any unreacted deposited species and to relieve any
internal stress as deposited. The Rupture Modulus of the resulting
material was 1030 kPa, and the hardness 3800 HV.sub.500.
The experiment was repeated without preheating the gas streams and
the resultant deposit consisted of poorly bonded, cracked, coarse
grain crystals, too weak to make strength or hardness
measurements.
EXAMPLE 14. AlN
The experiment of example 13 was repeated using the following
conditions: 92 ml. per minute of aluminum chloride was mixed with
300 ml. per minute of hydrogen. The total pressure in the chamber
was 300 torr. The mixed stream of the aluminum chloride and
hydrogen was heated to 600.degree. C. and then mixed with a
preheated stream of 50 ml. per minute of ammonia. At a substrate
temperature of 1060.degree. C., a deposition rate of 0.25 microns
per hour was achieved. The resulting deposit was smooth, having
average grain size of 0.1 microns. The X-ray diffraction showed the
material to be stochiometric aluminum nitride. The hardness of the
deposit was 1600 HV.sub.500.
EXAMPLE 15. Al.sub.x O.sub.y N
The above experiment (Example 14) was repeated under identical
conditions except that 50 ml. per minute of carbon dioxide was
added to the preheated mixed stream. A similar fine grain deposit
resulted except that the hardness was increased to 2400HV.sub.500.
The deposit is believed to be on alloy containing Al, O, and N.
EXAMPLE 16. Si.sub.x N.sub.y O
An experiment was conducted in which a stream of 140 ml. per minute
of silicon tetrachloride was mixed with a like amount of hydrogen
preheated to 700.degree. C. and thence mixed with a preheated
stream of 70 ml. per minute of ammonia plus 15 ml. per minute of
oxygen. The graphite rod part temperature was held at 1400.degree.
C. by induction heating. The total pressure was 50 torr. A deposit
containing silicon, nitogen and oxygen was made at a rate of 0.5
mm. per hour. Deposits had grain size of less than 0.5 micron.
EXAMPLE 17. Si.sub.x Al.sub.y O.sub.z N
An experiment was conducted in which a stream of 600 ml. per minute
silicon tetrachloride, 100 ml. per minute of aluminum trichloride,
800 ml. of hydrogen were preheated to 700.degree. C., and
subsequently mixed with a preheated stream of 100 ml. per minute of
ammonia and 20 ml. per minute of oxygen. The total pressure in the
chamber was 50 torr. The graphite rod substate was was held at
1325.degree. C. A dense fine-grain, coherent deposit containing
silicon, aluminum, oxygen, and nitrogen was made at a rate of 0.25
mm per hr. The deposit showed an X-ray diffraction pattern of beta
silicon nitride and was, therefore, presumed to be a material,
reported by several investigators, as beta SIALON.
EXAMPLE 18. ZrB.sub.2
Example 1 was repeated except that the interior of 0.938 cm
Zircalloy tubes, 15 cm long, were coated with ZrB.sub.2. The
surfaces of the tubes were first boronized using a mixture of 100
ml/min of BCl.sub.3 and 4600 ml/min of H.sub.2. The pressure was
250 torr and the temperature of the tubes was 950.degree. C. After
15 minutes, 400 ml per minute of Cl.sub.2 as added to a heated
zirconium metal chip bed. The zirconium ignited and the effluent
gas, believed to be ZrCl.sub.3 was added to the deposition gas
stream. After 30 minutes, the Cl.sub.2 flow was increased to 800
ml/min. The resultant deposit was a bright metallic coating of 40
mm thickness having a hardness of HV.sub.500 of 7500.sup.kg
/mm.sup.2. The total time for experiment was 45 minutes.
If a substrate cannot be heated by the passage of an electrical
current through the substrate or by induction heating, a hot wall
reactor, such as used in Examples 11, 12, and 13, is used to supply
the necessary heat to the system. When using a hot wall reactor, it
was found that the ratio of other reactants and gas streams had to
be modified to achieve satisfactory results as compared to the
ratio of reactants and gas streams used with substrates which were
heated by an electrical current or by induction. Such modifications
are readily determined empirically by trial and error and are
within the ordinary skill of the art.
In addition to the superior coatings produced by the CNTD method of
the present invention, the CNTD method has also been found to be
advantageous in terms of the temperature and rate at which the
deposits are produced. It is well known that titanium carbide
deposits made by conventional CVD are reqularly conducted in the
range of 900.degree. C. to 1200.degree. C. and require several
hours to produce a coating in the order of 10 microns in thickness.
The CNTD method, however, has been able to produce superior
titanium carbide deposits of 10 microns in thickness at
temperatures as low as 750.degree. C. in as little time as about 40
minutes.
In practicing the present invention, best results in terms of
producing a hard deposit and reproducibility of results were
achieved using the halides of aluminum, titanimum, zirconium,
hafnium and silicon as the source of the metallic component of the
hard metal alloy deposited on the substrate. The halides of
columbium, tantalum and boron were also found to work as the
metallic component but not as well as aluminum, titanium,
zirconium, hafnium or silicon. Results using the halides of
columbium, tantalum and boron were not always uniform. Results
using the halides of columbium and tantalum were improved when the
halide is reacted with a silicon halide to produce a hard metal
alloy on the substrate.
The invention provides an improved method for producing a coated
substrate, as well as improved quality coated substrates. By
providing an intermediate liquid phase on the surface of the
substrate being coated, pyrolyzing this liquid or reacting a gas
therewith to produce the final coating composition, the structure
of the coating composition is such as to provide superior physical
qualities. The deposits of the invention are smooth surface fine
grained randomly distributed crystals free of columnar orientation
and having a very high modulus of rupture. Other metal and
semi-metal systems can also be effectively improved in their
deposit quality in accordance with the invention. Parameters
necessary to do this are readily determinable by those skilled in
the art from the information contained herein combined with that
contained in "Techniques of Metals Research" R. F. Bunshah, Ed.,
Intersciences Publishers, Div. of J. Wylie and Sons, New York, New
York, 1968, Volume 1, Chapter 33.
Various modifications of the invention in addition to those shown
and described herein will become apparent to those skilled in the
art from the foregoing description and accompanying drawings. Such
modifications are intended to fall within the scope of the appended
claims.
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